The present invention relates generally to air dryers, and more specifically, to an air dryer with an integral pre-charge volume for a brake system for vehicles.
Air dryers employing membranes consisting of a permeable membrane capable of blocking the passage of nitrogen and oxygen molecules, but allowing water vapor molecules to pass through, as described in U.S. Pat. Nos. 6,719,825 and 5,525,143 amongst many others. In one variation of the technology, the air to be dried passes through the center of the membrane element. The membrane permits the passage of the water vapor to the outside of the membrane, but prevents the passage of the air to the outside of the membrane, thereby drying the air.
To work effectively, the outside of the membrane must be kept dry and at a lower pressure than the inside, creating the partial pressure differential to drive the water vapor out. This is done by providing some fraction of the dry output air as a counter flow sweep air across the outside of the membrane. The sweep air can be provided by sweep air orifice(s) connecting the dry air in the membrane air dryer outlet to the sweep air chamber surrounding the outside of the membrane. The orifices control the volume of sweep air, typically 10-20% of the dryer capacity and create a pressure drop in the sweep air volume. The sweep air and entrapped moisture are expelled to atmosphere.
U.S. Pat. No. 6,719,825 shows a control valve at the inlet for the sweep air. U.S. Pat. No. 5,375,620 shows a self-adjusting flow metering device for the sweep air. U.S. Pat. No. 5,525,143 shows an outlet chamber in the membrane dry housing for re-directing a portion of the dried air for the sweep air before exiting the dry housing. U.S. Pat. No. 6,719,825 shows a more complicated structure for re-directing a portion of the dried air for the sweep air using an auto-purge metering device or valve.
The present disclosure is directed to an air dryer, for example, for locomotives, packaged to fit inside a reservoir. The air dryer is generally cylindrical with a circular mounting flange on one end, which bolts to a similar mounting flange welded to the end of the reservoir. This arrangement solves the problem of finding room for the air dryer between main reservoir #1 and #2 on a locomotive, protects the air dryer and especially the vulnerable membrane element from the very high ambient temperatures (as high as 300° F.) during operation of the locomotive in tunnels; protects the air dryer from environmental hazards, like flying stone ballast; eliminates installation piping, and minimizes weight.
Such a membrane air dryer includes a housing with an air inlet, an air outlet, a sweep air inlet and a sweep air outlet; and a membrane separator having surfaces extending between and having an inlet and an outlet respectively connected to the air inlet and the air outlet. A sweep air passage in the housing extends between first and second ends of the membrane along and includes surfaces of the membrane. The sweep air passage has an inlet adjacent the air outlet and has an outlet adjacent the air inlet and connected to the sweep air outlet. A volume is concentric to the membrane separator, has an inlet connected to the outlet of the membrane separator and has an outlet connected to the sweep air inlet.
The membrane air dryer includes a valve connecting the outlet of the volume and the inlet of the sweep air passage. A first passage in the housing connects the valve and the sweep air passage's inlet and the first passage extends between the inlet and outlet of the membrane separator. The volume extends between the inlet and outlet of the membrane separator. The inlet of the volume is adjacent the membrane separator's outlet and the outlet of the volume is adjacent the membrane separator's inlet.
The dryer housing may be mounted in the inlet of a reservoir and extends from the reservoir inlet into the interior of the reservoir so that the housing's air inlet is the inlet of the reservoir, the housing's air outlet, the sweep air passage's inlet and the volume's inlet are interior the reservoir and the sweep air outlet of the housing is exterior the reservoir. The membrane separator and the volume are interior the reservoir. A valve connects the outlet of the volume and the inlet of the sweep air passage and the valve is exterior the reservoir.
In a vehicle brake system including a brake controller and the reservoir with the air dryer, the brake controller controls the valve. The controller controls the valve to proportion the sweep air flow to air flow through the membrane separator.
A combination of a reservoir having an air port and a membrane separator having a housing with a separator member between an air inlet and an air outlet, a sweep air passage having an inlet and an outlet and a volume connecting the separator member's outlet to the sweep passage's air inlet. The housing extends from the reservoir's air port into the interior of the reservoir so that the housing's air inlet and sweep air passage's outlet are exterior the reservoir and the housing's air outlet, the membrane separator and the volume are interior the reservoir. A valve connects the volume and the sweep air passage's inlet, and the sweep air passage's outlet is connected to atmosphere.
These and other aspects of the present method will become apparent from the following detailed description of the method, when considered in conjunction with accompanying drawings.